I have a Bonneville 1963 trying to id the engine. The number is 276803 YC.
is there anybody out there who can tell me what kind of engine that is, have a feeling that its not the original :?:

On my old pick-up that was a 79 I took the numbers to the dealer and they were able to tell me the information from them. Some of mine were stamped bad and some were not legible anymore. All I got from myine was the casting year. You are talking about the numbers in the block right? I know for the 350 it was on a tab just below one of the heads on the front of the engine.

Found this

http://www.yearone.com/updatedsingle...gineinfo1.html

Note the very last line of the first page.

For old GM casting numbers www.mortec.com is a great resource. But, they don't have much for casting numbers other than Chevy blocks. IIRC, there'* an area where you can post a question. It might not hurt to check out that site to see what you can learn.

Lots of good information on the Wallace Racing site. It is a frame page and only works correctly for me using Internet Explorer.
http://www.pontiacracing.net/
On the home page click on "Enter"
On the next page click on the "Info" link on the left
Then select the "engine codes" page and that should get you well on your way to identifying your engine.

Also, if you haven't found them yet, check out Performance Years and Classical Pontiac. Between those two sites, it is quite possible that you will find a previous owner or someone who has actually worked on the car you own.